Various types of heat engines have been designed that perform useful work by extracting a portion of the energy that exists in a heat source relative to an environment. In a general sense, these engines often convert the microscopic kinetic energy of molecules to a macroscopic form of energy that can be utilized to perform work, such as moving a vehicle, pumping water, or rotating the armature of an electric generator.
One engine, the reciprocating steam engine, was used in early automobiles and locomotives because of the simplicity of design, flat torque curve, and multiple fuel capability. Such steam engines were inefficient and may have only had an efficiency of 8-10%. Therefore, internal combustion engines superseded steam engines because of their better thermodynamic efficiency and ease of use.
Internal combustion engines have provided good service as prime movers for transportation and auxiliary power sources, however, they have significant weaknesses. For example such engines are noisy, polluting, have narrow speed/torque characteristics, have stringent fuel chemistry requirements, have concentrated thermal signatures and are high maintenance. A typical gasoline internal combustion engine may have an efficiency of 15-30%, and a diesel engine may only be 25-40% efficient.
In an attempt to address the many inadequacies of the internal combustion engine, engineers formulated the idea of an external combustion rotary heat engine. Such engines in comparison with other types of heat engines, offer quietness and low pollution. Furthermore, external combustion rotary heat engines may offer simplicity and improved efficiency. Rotary heat engines, however, have never been commercialized because of certain short comings.
For example, some rotary heat engines/heat pumps have heat transfer structures that have not been optimized to promote nucleate boiling and dropwise condensation, and their primary energy sources have not been optimized to produce a high energy density. Such engines typically utilize convection or forced convection as the primary heat vector. In these engines, fins, staggered heat exchange tubes, and fan blades are provided to increase convective interaction with the hot side gases and to provide high thermal conductivity. Many of these engines operate in a temperature regime where the Newtonian cooling law describes the predominate heat delivery mechanism Q=h×A×ΔT, where h=heat transfer coefficient (100 W/m2K for force convection air). At a 1000° C. temperature differential, approximately 100 Kw/m2 can be convectively delivered to a conductive receiving surface. Therefore, these engines are very limited, and would require very large rotating heat absorption surfaces. For example, an automotive engine of 30 Kw operating at 30% thermal-to-work efficiency would require 1 m2 of emitter/absorber surface areas. The need for this overly large rotating heat absorption structure has prevented the development and deployment of this type of engine.
Additionally, rotating heat engines/heat pumps do not completely utilize the rotating nature of the engine/heat pump. For example, synergy has not been developed between output waste heat and the possible uses of the energy contained in the waste heat output, and the combined thermodynamic cycle capability of the rotating engine/heat pump has not been developed and exploited. There is some mention of incorporating fins or blades to help move the external cooling fluid through the engine, however, the idea of using the rotating heat rejecter structures to produce thrust has not been developed. Accordingly, a rotating heat engine that incorporates heat rejecters capable of using a predetermined portion of the rotative energy to develop thrust, preferably combined with the expansive force of a heat rejection fluid, would further the development and deployment of a rotary heat engine.
If a rotating engine is to be of practical value it must be manufacturable, cost effective, and have a volume and mass power density that permits its use in typical applications, such as, automotive, aerospace, commercial, and industrial applications. To fulfill these requirements, energy must be transformed, delivered, and made to do work at a rate that compares favorably with traditional engines.